Why does MEX require transiting travelers to go through immigration?
 

I had a connecting flight in MEX coming from IAH on my way to a different country. My layover was less than 1:30 hours. It was interesting to me all travelers are required to go through immigration even if you're not visiting MEX.

It seems kinda pointless and a waste of time and money.

I know this is standard at US airports, but are the many other countries doing this nowadays?

It happens in the EU at the first airport where you land coming from the US even if your destination is elsewhere.

I have had to do it before in a few countries

Normally at EU airports, it happens only if you're continuing to a country within the schengen zone, where you don't do immigration upon entering that country. Of course there are some exceptions if you must change terminals, including at LHR (which is EU but not schengen).

Why does MEX require transiting travelers to go through immigration?
 

What puzzling to me is the possibility of transiting for a county that requires a visa in advance? What if I'm passing through Zambia on my way to Madagascar, and Zambia requires a pre approved application?

Is there a compiled list of countries where this may be an issue?

USA :td: